what kind of capacitors would i use to store a 12v charge for 15 seconds

Just scour the internet for circuits... solar garden lights etc. There are plenty of simple circuits you can experiment with and build to get you started with. Once you've got the basic ideas you can advance to more elaborate projects. Solar panels can be connected to increase voltage outputs (series) or to increase current delivery (parallel) by using a combination you can get the ideal voltage and current for your own needs. I wish you all the best in your quest... Regards

It's easier to change the load to match the source rather than convert the source. As in - change your led lighting to run on 5 volts instead of 12 - then run on 5ish volt batteries. Otherwise - you need to 'boost convert' the output from the solar cells to 12 volts and charge 12 volt batteries. Capacitors would be prohibitively expensive to use in this application.

im trying to get into electronics, specifically green energy and just trying to learn how every thing works and how to put it together so it does work. so ur saying the small capacitors arnt what im looking for. how would i increase the output from my solar cell to get to 12 v i have scavenged several 18 wheeler lights from the side of the road that are led and they only work on a 12v system how would i decrease them to 5v